Not able to read /dev/input/mice

MHermann

Hi all,
I am trying to get information about mouse events.
Therefore I did the following:

...
void MyClass::init(void)
{
    m_file = new QFile("//dev/input/mice");
    if (!m_file->open(QIODevice::ReadWrite)) {
    }
    else {
        m_notifer = new QSocketNotifier(m_file->handle(), QSocketNotifier::Read, this);
        connect(m_notifer, SIGNAL(activated(int)), this, SLOT(readMouseData(int)));
    }
}
...
void MyClass::readMouseData(int socket)
{
    QByteArray mouseData = m_file->readAll;
}
...

If I click or move the mouse, the socket notifier calls readMouseData().
But then I have the problem that all hangs up at readAll(). readAll() does not return.
Does anyone know what the problem is?

sierdzio

Since it's not a regular file some methods might not work. Check the docs, it's usually explained there.

Try connecting a data stream to it and reading it this way.

ChrisW67

Does using the QIODevice::readyRead() signal not work on this?

Observations:

The path is /dev/input/mice which may cause issue.
An unprivileged user will not be able open this file on many systems (My Ubuntu machine for example).
You are not likely to to write to this file, so why open ReadWrite?

JonB

@ChrisW67
Purely OoI, without sidetracking topic so briefly, what exactly is /dev/input/mice and what's it for anyway? :) [Not to mention, how many multiple mouses are supposed to be attached?]

SGaist

@JonB if memory serves well, it's a "multiplexer" device that is to be considered a hack to be used by older applications. It's a permanent device that gets the signals from the other mouse/tablet devices. Useful in the case of mouse hot plugin for applications that cannot handle them.

MHermann

@ChrisW67:

I did not try QIODevice::readyRead()
I corrected the path to "//dev/input/mice"
User has privilges. The user belongs to the group input.
ReadWrite-access is not necessary. I used it during my tries to get it run. I changed it back to readOnly.

MHermann

Now it is working.
If someone is interested, here are the code snippets:

...
void MyClass::init(void)
{
    m_file = new QFile();
    m_file->setFileName(m_filename);
    if (!m_file->exists()) {
        qWarning("file does not exist");
        return false;
    }
    else {
        m_fd = open(m_filename.toUtf8().data(), O_RDONLY|O_NONBLOCK);
        if(m_fd==-1) {
            qWarning("can not open file");
            return false;
        }
        else {
            m_notifier = new QSocketNotifier(m_fd, QSocketNotifier::Read, this);
            connect(m_notifier, &QSocketNotifier::activated, this, &MyCursor::readMouseData);
            return true;
        }
    }
}
...
void MyClass::readMouseData(int socket)
{
    qDebug() << "***** readMouseData() *****";
}
...

JonB

@MHermann
At one point you asked about the data/struct returned when you read from /dev/input/mice, though you seem to have removed that question now. Did you see e.g. https://stackoverflow.com/a/23317086, which seems to show it generates "messages" which are 3 bytes long? Or there is a struct input_event in #include <linux/input.h>? There is also a suggestion that nowadays you are supposed to use /dev/input/event# instead, but I leave it to you.